Many well-trained athletes and women who diet excessively have primary or secondary amenorrhea, or other disturbances of ovarian function. These women also display abnormalities of the pulsatile secretion of gonodotropin releasing hormone (GnRH) by the hypothalamus. Both of these phenomena are associated with changes in relative adiposity due to loss of body fat, increased muscle mass, or both. The effect is reversible and weight gain or cessation of the exercise can restore normal ovarian function after varying periods of time. A unique opportunity to test the hypothesis that changes in relative adiposity are causally related to the changes in ovarian function is provided by the development of magnetic resonance imaging (MRI). MRI is non-invasive and makes possible the evaluation of both internal and subcutaneous fat in the entire torso by the use of a whole body coil. Chemical shift imaging techniques can also be used to measure the aliphatic proton peak line width of particular fat depots. The objective of this research proposal is to investigate the effects of two contrasting training periods, low intensity and high intensity training, of 20 elite oarswomen on their relative adiposity, ovarian function and estrogen metabolism. In each training phase the following measurements of each athlete and 10 non-athletic controls will be made: 1) Whole body fat (thoracic, abdominal, pelvic and femoral) by magnetic resonance imaging (MRI); 2) Lean body mass directly by D20 and indirectly by Bioelectrical Impedance Analysis; 3) Ovarian function will be monitored by urinary pregnanediol glucuronide, urinary estrone glucuronide, salivary progesterone and basal body temperature; 4) The extent of 2-hydroxylation of 17 beta-Estradiol by radiometric analysis; 5) fasting ketone bodies and free fatty acids. In addition to providing insight into the hypothalamic control of ovarian function, the proposed study may have significance for the public health, since former athletes with long term training have a significantly lower life time occurrence of cancers and benign tumors of the breast and reproductive system.